The glaucophytes, also known as glaucocystophytes or glaucocystids, are a small group of rare freshwater microscopic algae.[1] Together with the red algae (Rhodophyta) and green algae plus land plants (Viridiplantae or Chloroplastida), they form the Archaeplastida. However, the relationships among the red algae, green algae and glaucophytes are unclear,[2] in large part due to limited study of the glaucophytes.

The glaucophytes are of interest to biologists studying the development of chloroplasts because some studies suggest they may be similar to the original algal type that led to green plants and red algae.[1][3]